In modern societies, multimedia in daily life is rapidly developing and ITS (Intelligent Transport Systems) such as ETC device used in toll roads and GPS becomes widely used. In order to treat the extraordinary increase of information and telecommunications technologies, the frequency of signals used for the transmission is becoming higher.
As material used for the information communication devices employing such a high frequency, engineering plastics which exhibit excellent dielectric properties in high frequency regions (especially in gigahertz bands) attract attention. The engineering plastics also exhibit good productivities and lightweight properties and therefore, they are expected to be applied for chassis and package of communication devices and electronic devices as well as for dielectric body and the like.
Among the engineering plastics, thermotropic liquid-crystalline polyester resin (which is called as liquid-crystalline polyester resin or LCP hereinafter) has the following excellent properties and is especially expected to be suitable for manufacturing devices which use high frequency signals:    (1) excellent dielectric properties: the relative permittivity (∈r) is constant in the frequency regions employed and dielectric loss tangent (tan δ) is small,    (2) good physicalities: mechanical properties including low-expansion property (dimensional stability), heat resistance, flame retardancy and rigidity are good, and    (3) good molding flowability: which allows processing of molded articles having down-sizing and thinner parts.
Among the liquid-crystalline polyester resins, wholly aromatic liquid-crystalline polyesters comprising 6-oxy-2-naphthoyl repeating unit, 4,4′-dioxybiphenyl repeating unit and aromatic dicarbonyl repeating unit in certain proportions are recently proposed because they exhibit good dielectric properties, heat resistance and molding processability (see US Patent Application Publication No. 2004-152865 and US Patent Application Publication No. 2004-164282).
The liquid-crystalline polyesters disclosed in the above two references and Japanese Patent Application laid open No. 2007-154169 include a great amount of 6-oxy-2-naphthoyl repeating unit. Though such liquid-crystalline polyesters exhibit excellent dielectric properties, their mechanical properties such as impact strength are relatively poor.
Accordingly, a wholly aromatic liquid-crystalline polyester resin which exhibits excellent dielectric properties as well as good mechanical properties such as impact strength is desired.